What is navigation?
getting a person or craft from one place to another How eyes, common sense, landmarks navigation aids for accuracy Tools clocks odometer electronic aids "radio navigation aids" ground-based space-based who processes user's system that calculates position user's system processes some of information latitude and longitude what are they high accurate systems -> short wavelength -> LOS less accurate long wavelength -> not LOS early space-based systems U.S. Navy Navigation Satellite System "Transit" (1964) Russian "Tsikada" 2-D High accuracy frequency of fixes vary with lat once very 30 minutes to once every 110 minutes History 1960's fragmentation DOD NASA DOT all working on 3-D systems goals global coverage continuous/ all weather operation serve high-dynamic systems high accuracy Transit low dynamic systems New systems proposed Tranist variant Johns Hopkins Univiserty APL NRL working on Timation Air Force working on "System 612B" Army working on candidates in 1969 DNSS Defense Navigation Satellite System formed Various systems were integrated into "NAVSTAR GPS" Became just "GPS" run by GPS Joint Program Office in El Segundo CA. Current GPS fully operational accurate, continuous, global, 3-D position and velocity also distributes coordinated universal time (UTC) time 24 satellites 6 orbital planes 4 satellites per plane not geosynchronus world-wide network of monitoring stations Based on TOA Satellites have atomic clocks on board Two frequencies L1 1575.42 MHz L2 1227.6 MHz All satellites broadcast with psuedo random codes that don't correlate Two codes C/A course acquisition P(Y) precision code navigation data -> ephemeris data ranging data -> Time of Flight Receivers must have a local clock 3-D position requires four satellites (clock error) time or height reduces this TOA based localization (example) Beacon based system signal propogation time speed of signal Fog horn example Assume an accurate clock Speed of sound 335 m/s, 5 s, 1675 m draw one circle Two fog horn example assume pretty good previous estimate - solved Three foghorn example Let them do an example Errors Atmospherics Foghorn offset Interfering sounds introduce epsilon draw new circles introduce uncertain epsilon draw new circles Go through 3-D analog assume knowledge of satellite position one range -> sphere two range -> circle three range -> two points one is probably on the earth four ranges -> one point Back to GPS GaliLeo Eventually details on satellites